National e-Invoicing System (KSeF)

What is the National e-Invoicing System (KSeF)?

The National e-Invoicing System, known in Polish as Krajowy System e-Faktur or KSeF, is the central electronic invoicing platform operated by the Polish tax administration. It is used to issue, receive and store structured invoices in a standardised XML format. KSeF is regulated primarily by the Polish VAT Act and by technical documentation published by the Polish Ministry of Finance.

A KSeF invoice is not simply a PDF invoice sent by e-mail. It is a structured electronic invoice created according to a logical schema specified by the Ministry of Finance. The Ministry of Finance has published the FA(3) logical structure for KSeF invoices. This means that invoice data must be provided in predefined fields, which can be automatically validated, processed and exchanged between accounting systems, enterprise resource planning systems and the tax administration.

From a legal perspective, KSeF changes the way invoices are issued and received. Under the VAT Act, a structured invoice is generally treated as issued when it is sent to KSeF and as received when it is assigned a KSeF identification number, subject to detailed statutory rules and special procedures for system failures or offline modes. The KSeF number is therefore important evidence that the invoice has entered the official system.

How does KSeF work in practice?

In practice, a business prepares invoice data in its accounting or ERP system, sends the data to KSeF through an API or another authorised tool, and receives confirmation from the system after successful validation. Once accepted, the invoice receives a unique KSeF identification number. The recipient can access the invoice in KSeF, provided that the relevant access rights and authentication mechanisms are in place.

KSeF requires companies to review more than the technical method of sending invoices. It affects contracting procedures, tax compliance, internal approval flows, access management, data quality, document archiving, correction invoices, payment processes and accounting controls. The system may also require changes to commercial contracts, especially where agreements specify the method of invoice delivery, the date of receipt of an invoice or payment deadlines calculated from receipt.

The implementation schedule has been subject to legislative changes and official postponements. According to communications of the Polish Ministry of Finance and amendments to the VAT Act, mandatory KSeF implementation has been introduced in stages, including the date of 1 February 2026 for the largest taxpayers and 1 April 2026 for most other taxpayers, with the PLN 200 million sales threshold, calculated by reference to 2024 sales including VAT, used to identify the first group. Because transitional provisions and exemptions may apply, each business should verify its status against the current VAT Act, implementing regulations and official Ministry of Finance guidance.

Who is affected by KSeF?

KSeF is relevant mainly to taxpayers issuing or receiving invoices connected with Polish VAT reporting. This includes Polish companies, branches, sole traders and, in some cases, foreign entities with a Polish fixed establishment involved in a transaction. The exact scope depends on the taxpayer’s status, the nature of the transaction and the type of invoice.

Not every document is treated in the same way. Consumer invoices, invoices issued through cash registers, invoices involving foreign counterparties, self-billing, corrected invoices and special-sector invoices may be subject to separate rules, exclusions or transitional arrangements. For this reason, KSeF implementation should not be limited to a general software update. It should include a legal and tax review of the company’s invoicing model.

When should a business seek legal support with KSeF?

Legal support is advisable when a company needs to determine whether it is covered by mandatory KSeF, how the system affects its contracts, and how to manage liability for incorrect or delayed invoices. This is particularly important for businesses with high invoice volumes, complex supply chains, cross-border transactions, shared service centres, multiple ERP systems or decentralised invoicing teams.

A quick legal and tax consultation can help identify errors before KSeF becomes a source of disputes. Typical risks include incorrect invoice classification, missing mandatory data, unclear invoice receipt dates, inconsistent payment terms, lack of proper authorisations, improper access to invoice data, or failure to update internal procedures. These issues may lead to tax exposure, contractual disputes, delayed payments, reporting inconsistencies or financial losses.

KSeF also raises compliance questions relating to personal data, cybersecurity and governance. Companies should define who may issue, view, download or correct invoices in KSeF, how authorisations are granted and revoked, and how evidence of invoice circulation is retained. In larger organisations, this often requires cooperation between legal, tax, finance, IT and operations teams.

Legal support in relation to KSeF

The support of a law firm in the area of KSeF and electronic invoicing may include in particular:

assessment of whether and when the company is subject to mandatory KSeF obligations,
review of invoicing models, document flows and VAT-related procedures,
analysis of contracts in terms of invoice delivery, receipt dates and payment deadlines,
preparation or update of internal KSeF policies and approval procedures,
support in allocating responsibilities between finance, tax, legal and IT teams,
assessment of risks connected with incorrect, late or rejected structured invoices,
advice on KSeF authorisations, access rights and governance,
support in disputes concerning invoice receipt, payment obligations or tax consequences,
coordination of KSeF implementation with broader tax compliance and reporting obligations.

Need support with KSeF implementation or invoice-related legal risks? Contact us.